I am no longer willing to pay a ridiculous amount of gold for identifying all my items by a shop keeper. I have 2 fighters, 2 rogues , a priest and a wizard in my group. the priest joined the guild already. How can I achieve that someone of my party is able to identify the items found??

and by the way, what specialization and when would you recommend for my 2 warriors and my 2 rogues?

Well, for a priest to do it, you have to be at least level three in the priest's guild to learn ancient lore, and four to learn cabalist. (So you can cast bless on your items.) And, as Wyv said, the more artifact skill you have, the more stuff you can ID.

Well, you have to get the blessings skill. That's what you use to bless items in the church. Personally I think you should be able to pay Mr.Highlevelpriest to bless yer gear, but noooo..

You basically have to do the guild quests to get up to level 3 (has nothing to do with character level) an then get the artifacts skill (Believe ya need ancient lore first). The higher yer guild level, the better some of the skills that become available to ya.

And you can only train (far as I've seen) one skill per guild per level. Once you level, you can train something again. It gets expensive.